Added missing API end points to the client

This change adds the following commands, which were
not previously present.
    $ openstack congress datasource list
    $ openstack congress datasource rows list
    $ openstack congress datasource rows list --trace
    $ openstack congress datasource tables list
    $ openstack congress policy tables list

Closes-bug: 1368334
Change-Id: Ic4ea722a5fb31eb43dc7af4bde0cd28bbc8f47a1